Definition: When a recipe calls for butter to be “softened,” the butter should be at a cool room temperature, somewhere between 68–72°F/20–22°C.
When It’s Used: Softened butter is used when it will be creamed with sugar in a recipe. The butter needs to be softened so that it will hold a web of air after being beaten with the sugar.
Tips for Softening Butter: Butter can easily be softened by being left to sit out at room temperature for 30–45 minutes. Butter will soften more quickly if it is cut up into small pieces.